1. Field of the Invention
This invention relates to a medicament inhalator, and more particularly, to a dry powder medicament inhalator usable by asthmatics and the like. By inhaling on a mouthpiece, a prescribed dosage of the medicament compressed within a disc housed within the inhalator is entrained in an air stream and inhaled by the user through the mouthpiece to coat the lungs of the user.
2. Description of the Prior Art
Asthma and other respiratory diseases have long been treated by the inhalation of an appropriate medicament to coat the bronchial tubes in the lungs to ease breathing and increase air capacity. For many years the two most widely used and convenient choices of treatment have been the inhalation of a medicament from a drug solution or suspension in a metered dose aerosol, pressurized inhalator, or inhalation of a powdered drug generally admixed with an excipient, from a dry powder inhalator. With growing concern being voiced over the strong link between depletion of the earth's atmospheric ozone layer and chlorofluorocarbon emissions, use of these materials in pressurized inhalators is being questioned, while an interest in dry powder inhalation systems has accordingly been stimulated.
Small quantities of a fine particle, preferably micronized powder, are used mainly for therapeutic purposes in treating diseases of the respiratory tract. Powders of this type, such as salmeterol hydronapthoate, in quantities generally below 50 micrograms (mg) are added to the respiratory air of the lung of the patient. It has been found that the particles of active materials should have a particle size of less than 5 microns (.mu.) in thickness to insure that they penetrate deep into the lung. Thus, the metered dose must be atomized, aerosolized, or sufficiently broken up for inhalation by the patient to achieve the desired effect in the required dosage.
Presently, there are four different principal methods in use to provide fine particle powders without the use of propellants in the treatment of diseases of the respiratory tract.
The first method relies on the use of hard gelatin capsules which contain both a dose of the active material, and, in addition, potential adjuvants. The inhalator used by the asthmatic patient comprises a device for perforating or opening the capsule which is inserted into the inhalator when required. An air stream generated by a vacuum created by sucking action by the patient on a mouthpiece of the inhalator removes the powder contained within the opened capsule. The empty capsule is then expelled from the inhalator, which is then ready to receive the next capsule. Inhalators using this capsule-perforating technology or capsule-opening technology are shown in U.S. Pat. Nos. 3,906,950; 4,013,075; 3,807,400; and 3,991,761. In these inhalators, the capsule, when perforated, has both its ends held still during inhalation. The air stream which passes through it as a result of inhalation removes the powdered medicaments and is intended to remove all of the powdered medicament from the interior of the opened or broken capsule. However, it has been found that the air stream induced by the user-patient is generally insufficient in duration to remove the entire contents from the capsule which acts as a housing and in fact, impedes the removal of the medicament.
A further type of inhalator does not use individual capsules but instead is loaded with a package having a series of blisters equidistant from each other adjacent to its periphery. Each blister contains a fixed quantity of powdered medicament. As shown in EPO patent application publications EPO 211595 and 455463 along with EPO 467172 A1, when each blister is moved into a predetermined position, the blister is broken by a suitable opening device releasing the powder, which is then inhaled by the patient. It has been found that small water droplets of moisture contained within the depressions in the blister pack may cause agglomeration of the prepared medicament. Accordingly, when entrained in the air stream and inhaled by the user, the preferred particle size which can do the most good may not be readily achieved.
Another type of inhalator uses a container housing a quantity of medicament sufficient for several doses and is commonly known as the Draco Turbuhaler and is described in detail in U.S. Pat. Nos. 4,668,218, 4,667,668 and 4,805,811. The container includes a device for withdrawing the powdered medicament from the container and for preparing a dose for inhalation. The withdrawal and dose preparation includes a plate having a predetermined thickness and a certain number of cup-shaped or frusto-conical through holes. The plate can be moved by mechanical means from a position where a proportion of the holes are filled with powdered medicament taken from the container to another position in which the holes filled with medicament are located within a channel. Air flows into the channel as a result of suction provided by the patient on a mouthpiece in communication with the channel, to remove the powdered medicament from the holes. A scraper device is provided to level the powder in the plate holes and insures complete filling of the holes and consequently a constant dose. It has been found however that when suction is applied to entrain the medicament from one or more holes in the plate, not all the medicament is entrained but due to insufficient breathing capacity of the user and the non-cylindrical shape of the holes, some falls back into or never leaves the holes. Additionally, there is an agglomeration problem as mentioned previously. Accordingly, a vortex device has to be provided to aerosolize or atomize the agglomerated entrained medicament, even assuming the proper dosage leaves the holes in the rotated plate or disc.
The mechanical means for moving and indexing the perforated plate in the Draco Turbuhaler includes a rotatable knob fixed to the plate. Therefore, it is possible to present a double charge for inhalation as there is no indication of a charged state during use of the device. There is also the inherent waste of material in using a reservoir-type filling mechanism, which is never completely emptied and the device is gravity sensitive in that it must be maintained in a vertical, upright condition between uses because if inverted, most of the powder in the disc-sized holes will fall out, and be returned to the reservoir. Reindexing the device to fill the holes or perforations in the plate raises the possibility of overdosing the patient or losing count of a non-administered dose.
Another mechanical delivery system for a blister-type dry powder inhalator is shown in PCT application WO 93/12831. Air under pressure is driven by a piston continuously through a cylinder to impinge upon a microsized dose of medicament encapsulated on the periphery of a carrier disc. The air entrains the dry powdered medicament which is inhaled by a user. A similar delivery system is illustrated in German patent DE 4133274 A1 wherein a spring-driven piston delivers air into a chamber wherein it is admixed with dry powder medicament housed in the chamber and inhaled through a mouthpiece. But, in each of these systems, the air is continuously dispersed and dispensed through the powder in a steady stream, but not in a concentrated burst, thus substantially reducing its driving force along the outer reaches of the air stream, and subjecting the delivery of a full dose in part to the limited breathing capacity of the user or inhaler.
Finally, a process for supplying a medicament in a dry powder inhalator is disclosed in German Patent No. DE 4020571 A1 in which in manufacturing the aerosol, a velour or velvet-like material loaded with powder is introduced into a jet stream of air. The jet stream of air lifts the powder from the velour-like material by the Bernoulli effect, entrains the same, which is then inhaled by the user. The problem with this type of an arrangement is that the fibers themselves intermix with the medicament.
The present invention avoids many of the problems associated with the prior art, enabling a predetermined exact dose to be supplied through an inhalator with the ingested particle size of the powdered dose being formed for maximum beneficial efficiency.